The conventional steam iron can not generate steam when ironing the fabric materials at low temperature because the temperature at the bottom of iron plate is too low to evaporate the water dropped into the iron evaporating room. If the water in the evaporating room accumulates, it will flow onto the fabric through steam holes. Due to the scale remained in the evaporating room, the water will make the fabric dirty. In order to prevent the water from dropping onto the fabric and making it dirty, some steam irons adopt the water dropping resistance function. When the temperature of the plate is too low, the temperature sensing double metal sheet shall work and make the steam valve closed. This function can prevent the steam valve from being opened by mistake when ironing at low temperature. There are also some preferred steam irons, the double metal sheet, connected with the plate and installed at the steam valve, can control the open and close of the steam valve. When the temperature on the plate is high, the steam volume will increase, and on the contrary, it will decrease, preventing the dropping of water out of the plate. In regard to this method, tinny steam can be produced when at low temperature, but that small amount of steam can not make any effect when ironing. The experiments indicate that the watery steam at low temperature can stretch the fabric with good effects. Therefore, concerning the fabric which needs to be ironed at lower temperature, if it is ironed with the steam, the time of ironing could be reduced and obtain good effects.